Heating and air conditioning units for vehicles are commonplace in the art. Two main configurations are used, one being the centre stack configuration and one the lateral configuration. In the centre stack configuration, a heater core is close to transverse an input duct and in the lateral configuration, the heater core is close to parallel to the axis of the input duct.
Many such units have an input air duct of a relatively large cross-section. The input air duct has a divider which defines two passageways, one of which contains a heat exchanger receiving engine coolant and the other of which contains no such heat exchanger. The two passageways combine again downstream of the heat exchanger in a mixing space and the air from the mixing space is distributed to different locations in the vehicle. One or more flow control devices is associated with the passageways, for example at the point of division of the input air duct so as to control the proportion of air flowing through the heat exchanger by comparison with the flow of air direct from the input air duct to the mixing space. The flow control devices are usually capable of substantially closing the air passages so that either all air flow in the input duct passes through the heat exchanger or all air flow in the input duct passes through the direct passageway to the mixing space. Intermediate positions allow proportion control.
It is possible to use a single door-type flow control device pivoting about the division point of the input air duct so that the door can be selectively across the heat exchange passageway, across the direct passageway or intermediate the two positions. Such single door type arrangements can however make the heating/air conditioning unit unduly large and also affect flow performance. It is alternatively possible to arrange separate doors across each of the passageways; where the doors are centrally pivoted in a butterfly formation, space may be saved.
Modern power units may not provide coolant which reaches the high temperatures that were formerly available and would be advantageous in supplying to the heat exchanger discussed above, known hereinafter as a heater core. Another problem arises during the warm up period of the power unit as during this time the coolant may provide little or no heating effect in the heater core.
It has therefore been proposed to additionally provide an electric heating device in the heating unit, this typically being a positive temperature coefficient (PTC) heating device.
Inclusion of such heating devices has a disadvantage in that it may adversely affect the flow of air through the heater core, and may also substantially increase the space occupied by the heating unit.
Object of the Invention
It is therefore an object of the present invention to address the difficulties of the prior art.